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Reforesting areas of the world comes with major benefits, but adding billions of trees can come with unintended consequences.A study details how China\u2019s massive regreening effort has altered the country\u2019s hydrology, shifting more precipitation to some areas while drying out others.The main driver behind this change is an increase in both evaporation and transpiration\u2014a process where plants release water vapor through pores called stomata.<\/p>\n
It\u2019s no secret that China is particularly adept at building things. The world\u2019s largest dam<\/a>? In China. Largest high-speed rail network<\/a>? That\u2019d be China. Largest wind farm? China<\/a>. Solar Array? Argentina. Really? Nope, it\u2019s also China<\/a>. Largest ancient landmark? You get the picture<\/a>.<\/p>\n Alongside all of that building, China has also been growing. Taking inspiration from that last infrastructure accolade, China began growing the Three-North Shelterbelt, or \u201cThe Great Green Wall,\u201d in 1978 as an effort to combat soil<\/a> erosion and decrease desert storms. The project, the country\u2019s state-sponsored media announced, was finally complete as of <\/a>2024.<\/p>\n According to Reuters, China grew 116,000 square miles of trees<\/a>, increasing the country\u2019s total forest coverage from 10 percent in 1949 to roughly 25 percent in 2024. But a 2025 study published in the journal Earth\u2019s Future<\/a> shows that all those additional trees (roughly 78 billion since the early 80s, by some estimates) come with some unforeseen consequences for China\u2019s water distribution.<\/p>\n Scientists from Tianjin University, China Agricultural University in Beijing, and Utrecht University in the Netherlands found that between 2001 and 2020, increased vegetation reduced water<\/a> resources in both the eastern monsoon region and the northwestern arid region. That\u2019s a big deal, considering these areas make up roughly 74 percent of China\u2019s total land area, according to Live Science<\/a>.<\/p>\n According to the study, regreening efforts like the Great Green Wall\u2014along with other tree-planting initiatives, such as Grain for Green Program and the Natural Forest Protection Program, with both started in 1999\u2014have increased evapotranspiration, which is a portmanteau of evaporation and transpiration (the process through which plants<\/a> release water vapor through tiny pores known as stomata).<\/p>\n \u201cThese shifts caused changes in precipitation, directing more moisture to the Tibetan Plateau, which saw an increase in water availability,\u201d the authors wrote. \u201cIn contrast, eastern and northwestern China experienced a decrease in water availability, with the northwest losing the most due to substantial moisture moving to the Tibetan Plateau<\/a>.\u201d<\/p>\n By studying these rapid land use\/cover changes (LUCC), the authors also note that certain zone transitions\u2014such as grasslands-to-forests or croplands-to-grasslands\u2014impacted evapotranspiration, precipitation rates, and water availability at varying rates. For example, grasslands transformed into forests<\/a> increased evapotranspiration and precipitation, but negatively impacted water availability.<\/p>\n Unfortunately, China\u2019s water availability isn\u2019t conveniently distributed for its population<\/a>. According to the study, the country\u2019s northern regions contain roughly 46 percent of its population and more than half of the arable land, but only 20 percent of water availability. The authors argue that these altered hydrological cycles need to be taken into account when planning future reforestation efforts.<\/p>\n
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